This is a good news and another opportunity for Ancelotti to add the world cup to what he has achieved so far as a successful coach.
Ancelotti never won a world cup. It is the chance to win a world cup and complete his career with the most prestigious trophy in football. However, he is already one of the most successful coach in history even if he may fail to win a world cup title with Brazil.
The question is, is Brazil at that level where they can comfortably say that with Carlo anceloti that winning the world cup will be realistic? The squad is obviously there and with a combination of real Madrid and Barca players that are currently doing exceptionally well, a good coach like Carlo anceloti will make a lot of difference but I don't see it at the level of winning the world cup at his first season at the national team at Brazil.
Spain and Argentina still looks like a better team compared to Brazil in terms of the possibility of winning the champions league but if Carlo anceloti comes and is able to make that happen, it's going to show to a large extent that he's a greate coach and arguably the best coach in the world.